Pump drive

ABSTRACT

A membrane or piston pump drive comprises a stepping motor ( 2 ) and a rotary-to-linear conversion mechanism for converting the rotary movement into a translation movement ( 6 ). The rotary-to-linear conversion mechanism comprises a rotary member ( 4 ) and a piston member ( 7 ) intended to move a piston or a membrane of the pump. The stepping motor comprises a rotor coupled to the rotary member which engages the piston member ( 7 ) in order to drive it in an essentially linear reciprocating movement.

The present invention concerns a membrane or piston pump drive, with a stepping motor.

Drives of the aforementioned type are known and described for example in German patent DE 196 23 537 or American patent U.S. Pat. No. 4,326,837. Publication DE 196 23 537 describes a membrane pump comprising a piston making a reciprocating movement by means of a cam system driven by a stepping motor through gearwheels, this motor being controlled by a microprocessor.

Compared with pump drives with a continuous motor, the stepping motor has the advantage of making it possible, through electronic means, to better control the pumped fluid output, since the stepping motor allows fine control of the speed of rotation of the motor, and makes it possible to know the angular position of the rotor without requiring any external sensor for this purpose.

In pumps with a stepping motor the pumped fluid output can be varied by changing the speed of rotation of the rotor of the motor, which varies the reciprocating frequency of the piston coupled to the rotor through a cam mechanism. The variation in the reciprocating frequency of the piston may have a detrimental influence on the variation in pressure in the pumped fluid, depending on the harmonic frequencies of the hydraulic system in which the pump is placed and the degree of damping of the pulsations or other factors.

Another known means of varying the pumped output in membrane or piston pumps is the adjustment of the magnitude of movement of the piston by mechanical means, as described in European patent application EP 1 283 366. In the latter application, the magnitude of movement of the pistons is regulated by adjusting the eccentricity of the cams which move the pistons.

Mechanical adjustment of the stroke of the piston may adversely affect the bulk and complexity of the pump system and the possibilities of regulation.

An object of the invention is to provide a piston or membrane pump drive that can be regulated with precision over an extended operating range.

It is advantageous to provide a pump drive that operates with little vibration and pressure variation in the fluid discharged.

It is advantageous to provide a piston or membrane pump drive which is very precise and reactive in order to be able to modify the output of fluid discharged very rapidly.

It is advantageous to provide a piston or membrane pump drive that is versatile and compact.

Aims of the invention are achieved by the piston or membrane pump drive according to claim 1.

In the present invention, a membrane or piston pump drive comprises a stepping motor, a step-down device, and a mechanism for converting the rotary movement into a translation (or linear) movement comprising a rotary member and a piston member intended to move a piston or a membrane of the pump, the stepping motor comprising a rotor coupled, through the step-down device, to the rotary member which engages the piston or membrane in order to drive it in an essentially linear reciprocating movement, wherein the stepping motor and the translation device are adapted to perform a reciprocating angular movement of said rotary member over an angle of less than 360°.

The rotary-to-linear conversion device can comprise a cam element on the rotary part, engaging a complementary cam on the member with essentially linear movement.

The angle of rotation of the rotary cam element defines the magnitude of the linear movement of the piston member. Advantageously, the angle of rotation of the cam is regulated electronically by control of the stepping motor in the same way as the control of speed and acceleration of the motor, without requiring regulation of mechanical members. The output of the pump can thus be varied not only by changing the reciprocating frequency of the piston but also its magnitude by means of an electronic control for the stepping motor, which makes it possible to optimise the functioning of the pump over a wide range of values, that is to say for large and small outputs, by controlling the magnitude and/or the frequency.

Instead of a cam mechanism, it is also possible to use a connecting rod system, whereby the linear movement member is fixed by means of a pivoting articulation to the rotary piece at the output of the gearbox.

The transmission of the motor torque through the gearbox, which may be in the form of gear wheels, means that the rotor of the motor can make several turns before changing direction. This makes it possible to obtain a finer control of the angular movement, in view of the reduction in the movement through the gearbox, and to better control the deceleration and acceleration ramp, in particular when changing the direction of rotation.

Other aims and advantageous characteristics of the invention will emerge from the claims, description and accompanying drawings, in which:

FIG. 1 is a perspective view of a piston or membrane pump drive according to the invention;

FIG. 2 a is a plan view of the pump drive showing a first extreme position of the movement of the piston;

FIG. 2 b is a view similar to FIG. 2 a showing the piston in the second extreme position;

FIG. 3 is a view of the drive in the direction III in FIG. 2 b, with a support plate in addition; and

FIG. 4 is a section along the line IV-IV in FIG. 2 a with a support plate in addition.

Referring to the figures, a pump drive 1 comprises a stepping electric motor 2 with a wound stator 3 and a rotor 4, a step-down device 5, a device 6 for converting the rotary movement into an essentially linear movement, and a piston member 7.

The gearbox 5 comprises gearwheels 8, 9, 10, 11 effecting a reduction of the transmission ratio between the shaft 12 of the rotor and the output shaft 13 of the gearbox.

The rotary-to-linear conversion mechanism 6 comprises a cam element 14 fixed to the output shaft 13 of the step-down device and engaging a complementary cam element 15, in the form of a free wheel, mounted on the piston member 7.

The piston member 7 is mounted in a bearing 16 of a body or support 17 for the drive in order to guide the piston member in a translation movement along an axis A.

The cam member 14 is, in this example, in the form of an essentially flat disc comprising an opening 18 whose periphery 19, or at least a portion of periphery, has the function of a cam surface engaging the complementary cam element 15 mounted on the piston member 7 for the movement of the latter in a reciprocating manner when the rotary cam member 14 performs an angular reciprocating movement. The profile of the cam surface 20, defined by the angular position of each point on the surface and its radial distance with respect to the rotation axis of the member 14, defines the axial position of the piston member 7.

In the preferred embodiment, the first extreme angular position 20 a of the cam profile corresponds to an extreme axial position of the piston member and the other extreme angular position 20 b of the cam surface corresponds to the extreme axial position of the piston member in the other direction. The movement of the cam member between the extreme angular positions 20 a, 20 b therefore corresponds to the maximum amplitude of the piston member. The opposite surfaces 20 c, 20 d of the cam make it possible to push and pull the piston member without requiring a recoil spring, which reduces the wear by friction and decreases the number of components. The opposite cam surfaces also make it possible to effect high accelerations and decelerations.

The output of the pump may advantageously be varied by acting on the number of steps performed by the rotor of the stepping motor before the change in direction, by an electronic control counting the number of steps and controlling the deceleration, the stoppage and the acceleration in the other direction of the rotor of the stepping motor. It is also possible to vary the pumped output by varying the speed of movement of the piston member by electronically controlling the frequency of the steps of the stepping motor.

With the device according to the invention, it is possible to obtain an asymmetric speed profile of the reciprocating movement by controlling, by means of the electronic control, the movement in a rotation direction with a step frequency different from the frequency in the other direction of rotation. An asymmetric movement profile can be very advantageous for optimising the suction and expulsion of the liquid by the piston according to the characteristics of the pump and the hydraulic system, for example in order to avoid cavitation during suction and impacts or vibration during expulsion.

The use of a stepping motor has not only the advantage of allowing very reliable and precise electronic control of the amplitude and frequency according to a required speed profile, but also makes it possible to generate a high torque at relatively low rotation speeds.

Advantageously, the electronic control of the motor can be effected through a low noise motor driver in order to avoid the known resonances of the stepping motor and also to optimise the efficiency of the motor. It is therefore possible to reduce heating of the drive by varying the current according to the operating state, for example by cutting off the current when the motor is stopped, reducing the current during the suction cycle of the pump in the case of low pressure, and supplying a high or nominal current during the expulsion cycle of the pump in a situation of high hydraulic pressure.

The step-down device makes it possible to reduce the bulk of the motor while improving the acceleration and deceleration ramps of the motor, as well as the precision in positioning of the cam member, consequently the amplitude and frequency of movement of the piston member.

The step-down device also makes it possible to absorb impacts, in particular during changes in direction. In order to be able to withstand the high radial loads, the output shaft 13 of the step-down device is provided with a bearing in the form of a compact needle bearing 21. The complementary cam element 15 of the piston member 7 is also mounted on a bearing in the form of a needle bearing 22 in order to reduce the friction between the cam surface 20 and this part. It should be noted that the complementary cam element 15 has a diameter slightly less than the radial distance separating the surfaces of the opposite cams 20 c, 20 d, this small clearance preventing rubbing of the complementary cam element against the cam surface opposite to the engaging cam surface.

Instead of a cam system, it is also possible to convert the rotary movement at the output of the step-down device by a connecting rod system, that is to say where the piston member is connected to a disc fixed to the output shaft of the step-down device by an articulation coupled pivotally to the disc and to the piston member. It may be noted that the piston member does not necessarily need to perform a pure translation movement, provided that there is a movement component in a direction perpendicular to the overall plane of the membrane in order to vary the pump volume. 

1. A membrane or piston pump drive comprising a stepping motor (2) and a rotary-to-linear conversion mechanism (6) converting rotary movement into a translation movement, the rotary-to-linear conversion mechanism comprising a rotary member (4) and a piston member (7) intended to move a piston or membrane of the pump, the stepping motor comprising a rotor coupled to the rotary member, which engages the piston member (7) in order to drive it in an essentially linear reciprocating movement, wherein the stepping motor and the rotary-to-linear conversion mechanism are adapted to drive the rotary member of the translation mechanism in a reciprocating angular movement at an angle of less than 360°.
 2. The pump drive according to claim 1, wherein the rotary member of the rotary-to-linear conversion mechanism comprises a cam surface engaging a complementary cam element fixed to the piston member.
 3. The pump drive according to claim 2, wherein the cam surface is formed on the periphery of an opening formed in an element in the form of a disc fixed to the output shaft of the step-down device.
 4. The pump drive according to claim 2, wherein the cam surface (20) comprises opposite cam surfaces (20 c, 20 d) for pushing, respectively pulling the piston member without a recoil spring.
 5. The pump drive according to claim 1, wherein the rotor of the stepping motor is coupled to the rotary member through a step-down device (5).
 6. The pump drive according to claim 5, wherein the step-down device comprises a pinion on the output shaft of the rotor of the stepping motor, coupled through gearwheels to an output shaft of the step-down device which is fixed to the rotary member of the rotary-to-linear conversion mechanism.
 7. The pump drive according to claim 1, wherein the drive comprises an electronic control able to control the rotation amplitude of the rotor in each direction as well as the frequency of the steps, so as to generate an asymmetric speed profile, where the linear movement speed of the piston member in one direction of suction of the pump fluid is different from the speed of movement of the member in the other direction.
 8. A method of controlling a pump drive according to claim 1, wherein the pump fluid output is varied by modifying the amplitude of angular movement and/or the frequency of the steps of the rotor in each direction.
 9. The method according to claim 8, wherein the angular speed of the rotor in one direction is regulated so as to be different from the speed in the other direction in order to obtain an asymmetric speed profile for the suction and expulsion of fluid. 